Organic Light Emitting Display (OLED) has the advantages of self-luminous, low driving voltage, high luminous efficiency, short response time, high sharpness, high contrast, nearly 180° viewing angle, wide temperature range, flexible display, Large-area panchromatic display, etc., and is recognized as the most promising display device by the manufacturers.
The OLED can be divided, according to driving method, into two categories: passive matrix OLED (PMOLED) and active matrix OLED (AMOLED), i.e., direct addressing and TFT array addressing. Wherein, AMOLED contains pixels arranged as an array, belongs to the active display type, is with high luminance efficiency, and is usually used as a large size display device with high sharpness.
AMOLED is a current-driven device. When current flows through the organic light emitting diode, the organic light emitting diode emits light, and luminance strength is determined by the current flowing through the organic light emitting diode. Most existed integrated circuits (ICs) only transmit voltage signal, therefore the pixel driving circuit of the AMOLED has to convert a voltage signal into a current signal. A conventional pixel driving circuit of the AMOLED usually has 2T1C, that is, a structure composed of two thin film transistors and one capacitor, to convert the voltage into current.
Usually, a plurality of pixel separating banks are formed on a planarization layer of the TFT array substrate of the AMOLED display device nowadays, a plurality of pixel areas on the TFT array substrate are defined by the pixel separating banks, and OLED functional layer is printed on the pixel areas thereafter. Specifically, the OLED material in solution state is dropped into the pixel areas, and then, the OLED material is dried to obtain the OLED functional layer. Because the organic materials used for forming the pixel separating banks generally are hydrophilic or hydrophobic, the thickness of the OLED functional layer near the center of the pixel area is smaller than the thickness of the OLED functional layer near the boundaries of the pixel area when the OLED functional layer is formed by printing and the materials forming the pixel separating banks are hydrophilic, or the thickness of the OLED functional layer near the center of the pixel area is larger than the thickness of the OLED functional layer near the boundaries of the pixel area when the OLED functional layer is formed by printing and the materials forming the pixel separating banks are hydrophobic. That is, the thickness of the OLED functional layer is uneven. When the AMOLED display device based on the OLED functional layer above is driven to display, the luminance strength in the same pixel area would be different when the current flows through the OLED functional layer with uneven thickness, and the display quality is therefore affected.